1. Field of the Invention
Embodiments of the present invention are generally related to a high-power liquid-cooled pump and signal combiner and methods thereof for fiber optic applications. More specifically, embodiments of the present invention relate to a pump and signal combiner capable of conveying several kilowatts of pump laser power for kilowatt class rare-earth doped fiber amplifiers without suffering thermal damage.
2. Description of the Related Art
Generally, the optical power output of rare-earth doped fiber amplifiers is limited to within a one kilowatt regime. Efforts to bring such amplifier output into the high-power range (i.e., greater than one kilowatt) have been made, but have not yielded successful results for long-term operation due to number of component failures from thermal damage.
Achieving high-power output requires the use of laser-pump combiners capable of combining multi-kilowatt power levels of pump laser power, and delivering the pump radiation to waveguides such as low-index coated passive or gain fibers to convey the pump light. However, in known attempts, the absorption of significant levels of pump power by unwanted contaminants on the fiber surface, contaminants at splice points and/or absorption by the coating material, results in very large local temperature increases and often cause catastrophic damage of the pump and signal combiner.
Competing amplifier and pump combiner requirements make optimization of the overall amplifier performance difficult. In most fiber applications, it is desirable for the rare-earth doped amplifier to have a small outside diameter to maximize the overlap of the pump radiation with the rare-earth doped core of the fiber, and minimize the amplifier fiber length. However, a smaller outside fiber diameter of the pump combiner output requires a larger numerical aperture, by virtue of the brightness theorem, which increases the likelihood of stray radiation and unwanted local heating.
One significant reason current pump-signal combiner package designs fail when attempting to achieve high-power output stems from the fact that the tapered and pigtail fibers are being surrounded by substantially stagnant air. The presence of the air is inefficient, and generally insufficient, for the cooling of local heat spots. In addition, air is a very low-index surround medium, supporting high numerical aperture light which is often absorbed by the coating medium at the transition between air-surrounded and coating-surrounded glass, and further increasing the likelihood of failure due to thermal damage.
Thus, there is a need for a high-power pump and signal combiner with more efficient and effective thermal dissipation. This need can be met by liquid-cooled combiners.